1. Field of the Invention
The present invention relates to a connection state control device, a connection state control method, and a connection state controlling program, and more particularly, to a connection state control device that controls the connection state of each of a distribution device as a distributor of distribution information and relay devices connected to the distribution device located at the top, a connection state control method, and a connection state controlling program to be used for controlling the connection state.
2. Discussion of the Related Art
As the Internet connections for general households have become high-speed connections in recent years, network systems that distribute so-called content such as music or movies are being more and more widely spread. In such a network system, personal computers or the like at households are connected so as to form a network, with one distribution device as a distributor being at the top (the network seen from the viewpoint of connection states is referred to as “topology”). Content such as music or a movie is distributed from the distribution device via the network.
In such a network, the distribution device and the personal computers constituting the network are referred to as “nodes”. Recently, so-called broadband routers, broadband set top boxes, and the like having the functions of those nodes are available on the market.
Further, each distribution device distributes distribution information different from others, and the nodes belonging to hierarchies below the distribution device are designed to receive the distribution information from several distribution devices. One of the nodes is designed to perform a reproducing operation upon receipt of the distribution information of different types from the distribution devices. This distribution of different distribution information using distribution devices of different types is a kind of multicast distribution, and each of the distribution devices serving as distributors (or each transmission path used for distributing information from the distribution devices) is sometimes referred to as a channel as in conventional television broadcasting. In this distribution system, the address of each distribution device as a distributor and the information indicating which line (channel) is being used for distributing the distribution information are often managed in an integrated fashion by a so-called management server provided in the network. When there is a request for distribution of information stored at a node, the node inquires of the management server for the address of the distribution device as the distributor of the distribution information and the address of the closest node on the line through which the distribution information is being distributed. Using the addresses obtained as a reply from the management server in response to the inquiry, the node is newly connected to the line through which the distribution information is being distributed.
In a case where a node is to selectively receive information distributed from channels of different types, the node checks the distribution information (more specifically, each piece of music and each movie being distributed as distribution information are checked), and selects the desired distribution information. In this case, after the distribution information from a distribution device is viewed for only a very short period of time, switching to distribution information distributed from another distribution device might be repeated (the switching of distribution information in a short time is sometimes referred to as a zapping operation).
A conventional technique involving broadband routers and the like having the functions of the nodes is disclosed in the following patent document, for example:    Patent Document 1: Japanese Patent Unexamined Publication No. 2003-169089
In the above-described conventional network system, however, when the zapping operation is often performed in the multicast distribution, the line to which a node is connected is often changed through the frequent zapping operation. As a result, accumulation of distribution information in each node is started from zero every time lines are switched, and a certain period of time is required until the accumulation of distribution information necessary to start a reproducing operation is completed at each node. This hinders smooth line switching and reproduction.